The takeover of South Shore Hospital by Partners HealthCare could have happened as early as today, but leaders at the state’s largest health care provider are holding off on the move so they can negotiate with the state attorney general’s office, which has been investigating the proposed merger.

The state Health Policy Commission opposes the takeover by Partners, arguing that the nonprofit Boston hospital chain has failed to back up its claims that the deal would lead to better and lower-cost care for South Shore residents.

The commission was created in 2012 to rein in health care costs and doesn’t have the power to block mergers. State and federal regulators have not indicated that they would try to stop the takeover by Partners, which also wants to acquire Harbor Medical Associates, a physicians group on the South Shore.

Attorney General Martha Coakley’s office and Partners HealthCare released a joint statement on Wednesday afternoon, announcing Partners’ decision to delay the acquisition and both parties’ intention to keep talking.

“March 20 marks 30 days after the Health Policy Commission’s final report on the proposed transactions involving Partners HealthCare, South Shore Hospital and Harbor Medical Associates. The office of the attorney general and Partners are engaged in discussions concerning the transactions. While that process is ongoing, Partners has agreed not to close either transaction,” the statement read.

South Shore Hospital spokeswoman Sarah Darcy declined to comment on Wednesday’s action by Partners, but on Monday she told The Patriot Ledger that the Weymouth hospital remained committed to the merger and the belief that it will benefit South Shore residents.

In a meeting with Ledger editors on Monday, David Seltz strongly disagreed with that assessment.

Seltz, executive director of the state Health Policy Commission, defended the report his commission released last month, which said the merger would raise the price of health care and crowd out competition without markedly improving care.

“They have not met the challenge of showing how they’re going to deliver savings,” Seltz said Monday at the meeting with the Ledger’s editorial board at the newspaper’s Quincy office.

The review is the first for the health commission, which estimates that a merger would push costs up by $23 million to $26 million a year.

Partners, South Shore Hospital and Harbor Medical countered that conclusion, saying the commission relied on outdated information and that the merger would actually save $19.8 million a year.

It was almost two years ago that Partners first announced its intention to merge with the 378-bed Weymouth hospital. In July 2013, Partners’ Brigham and Women’s Hospital began the process of acquiring Harbor Medical Associates, which has 65 physicians working at several locations on the South Shore.